Pan D A, Mater M K, Thelen A P, Peters J M, Gonzalez F J, Jump D B
Departments of Physiology, Biochemistry, Botany, and Plant Pathology, Michigan State University, East Lansing, MI 48824, USA.
J Lipid Res. 2000 May;41(5):742-51.
The glycolytic enzyme, L-pyruvate kinase (L-PK), plays an important role in hepatic glucose metabolism. Insulin and glucose induce L-PK gene expression, while glucagon and polyunsaturated fatty acids (PUFA) inhibit L-PK gene expression. We have been interested in defining the PUFA regulation of L-PK. The cis-regulatory target for PUFA action includes an imperfect direct repeat (DR1) that binds HNF-4. HNF4 plays an ancillary role in the insulin/glucose-mediated transactivation of the L-PK gene. Because the fatty acid-activated nuclear receptor, peroxisome proliferator-activated receptor (PPARalpha), binds DR1-like elements and has been reported to interfere with HNF4 action, we examined the role PPARalpha plays in the regulation of L-PK gene transcription. Feeding rats either fish oil or the potent PPARalpha activator, WY14,643, suppressed rat hepatic L-PK mRNA and gene transcription. The PPARalpha-null mouse was used to evaluate the role of the PPARalpha in hepatic transcriptional control of L-PK. While WY14,643 control of L-PK gene expression required the PPARalpha, PUFA regulation of L-PK gene expression was independent of the PPARalpha. Transfection studies in cultured primary hepatocytes localized the cis-regulatory target for WY14,643/PPARalpha action to the L-PK HNF4 binding site. However, PPARalpha/RXRalpha heterodimers did not bind this region. Although both WY14,643 and PUFA suppress L-PK gene transcription through the same element, PUFA regulation of L-PK does not require the PPARalpha and PPARalpha/RXRalpha does not bind the L-PK promoter. These studies suggest that other intermediary factors are involved in both the PUFA and PPARalpha regulation of L-PK gene transcription.
糖酵解酶L-丙酮酸激酶（L-PK）在肝脏葡萄糖代谢中起重要作用。胰岛素和葡萄糖可诱导L-PK基因表达，而胰高血糖素和多不饱和脂肪酸（PUFA）则抑制L-PK基因表达。我们一直致力于确定PUFA对L-PK的调控作用。PUFA作用的顺式调控靶点包括一个与肝细胞核因子4（HNF-4）结合的不完全直接重复序列（DR1）。HNF4在胰岛素/葡萄糖介导的L-PK基因反式激活中起辅助作用。由于脂肪酸激活的核受体过氧化物酶体增殖物激活受体（PPARα）可结合类似DR1的元件，且据报道会干扰HNF4的作用，因此我们研究了PPARα在L-PK基因转录调控中的作用。给大鼠喂食鱼油或强效PPARα激活剂WY14,643，可抑制大鼠肝脏L-PK mRNA和基因转录。利用PPARα基因敲除小鼠评估PPARα在L-PK肝脏转录调控中的作用。虽然WY14,643对L-PK基因表达的调控需要PPARα，但PUFA对L-PK基因表达的调控与PPARα无关。在原代培养肝细胞中进行的转染研究将WY14,643/PPARα作用的顺式调控靶点定位到L-PK的HNF4结合位点。然而，PPARα/RXRα异二聚体并不结合该区域。尽管WY14,643和PUFA都通过同一元件抑制L-PK基因转录，但PUFA对L-PK的调控不需要PPARα，且PPARα/RXRα不结合L-PK启动子。这些研究表明，其他中间因子参与了PUFA和PPARα对L-PK基因转录的调控。
